Vista - HP Color 2605 has pink tint down middle of page

This is not specifically a Vista issue (although that is my O/S), but I'm
not sure where else to post. I have an HP ColorLaser jet 2605dn that I've
had for about a year and a half. Recently (the last month or so), prints
of photos are coming out with a slightly red "cloud" down the middle of the
image. It's not a clear-edged area, just like a slight red-tinted shadow
running about 3-4 inches wide along the middle of the page. Regular
printing (color or mono), Windows test pages, etc. all come out fine, it's
only pictures.

I've tried it with several sources, digital camera prints, scanned images,
etc. I also tried it with an image from an XP laptop and I got the same
effect, so it appears to be in the printer itself.

I was thinking it might be something in the Magenta cartridge, but the
cartridge has about 40% left, and I hate to replace it if I don't need it.

Any suggestions would be appreciated.